MBB 222 LEC 19 dna replication

simply, what does dna replication do? what it involves (3 main) and what must happen before every cell division

-maintain genetic info

-involve enzyme, protein, molecular machinery

-DNA must be DUPLICATED b4 cell division

replication ensures what

each daughter cell recieves a complete genome

what provides the basis for copying genetic info

complementary base pairing

what part of cell cycle is dna replication?

S (after G1, before G2)

3 hypothesized models of dna replication?

conservative: parental dna remains tgt (one daughter all new, one daughter all old)

dispersive: old/new dna mixed (looks patchwork)

semiconservative: each daughter dna has one old n one new strand (double helix have 2 diff color strands)

what did meselson-stahl experiment provide evidence for

that dna replication is SEMI CONSERVATIVE (each daughter have one old one new)

-technique: seperate dna w/ density CENTRIFUGATION. grow bacteria w/ heavy isotope, then switch to light isotope

5 components for dna replication

1. dna TEMPLATE

2. deoxy nucleoside tri phosphate (dNTPs)

3. RNA primer (short STRAND of nucleotides (made by primase) that base-pairs with dna TEMPLATE n provides starting point for dna polymerase to synthesize new strand

4. DNA polymerase (large PROTEIN complex, includes enzyme that catalyze addition of dNTPs on 3’ OH end of primer)

5. Mg2+ ions (cofactor for polymerase) (help POSITION incoming nucleotide for nucleophillic attack by 3’OH)

what direction dna polymerase synthesize DNA

5 to 3

what unwinds dna? what primes replication (what is that synthesized by)

-enzyme HELICASE unwinds dna (expose base on template strand)

-replicated primed by SHORT RNA PRIMERS (synthesized by primase (an rna polymerase)

-later primer removed and replaced by dna)

what do dna polymerases vs rna polymerases require to synthesize dna

-dna polymerase: pre-existing DNA or RNA primer + template (polymerase add incoming dNTPs to primer with 3’-OH)

-rna polymerase NEEDS NO PRIMER (synthesize from scratch by form phosphodiester bond)

why can rna polymerase start rna synthesis from scratch

can hold first 2 nucleotides in its ACTIVE SITE n catalyze first phosphodiester bond w/ out pre-existing 3’-OH

what 3 phosphates do incoming nucleotides contain as they enter as dNTP?

a, B, y